Progress 06/15/07 to 06/14/10

Outputs
OUTPUTS: A workshop was held on October 7, 2008 at the University of Florida to disseminate results from our research to extension service providers. It was attended by 30 participants. Participants were divided into smaller groups to interact with individual researchers using a roundtable format that allowed participants to ask questions of the researchers and to discuss the results that were presented. This format was again used on October 8 and 9, 2009, at a 2-day train-the-trainer workshop held at the University of the Virgin Islands Agricultural Experiment Station and included a tour of the Virgin Islands Sustainable Farm Institute. The workshop was attended by 25 agriculture sector service professionals, agricultural extension personnel, and local farmer group representatives. The purpose was to educate and provide an opportunity for interactive dialogue on production issues facing tropical sustainable agricultural production in the U.S. Virgin Islands and to specifically focus on the utility of cover crops and rotations for pest incidence and soil management in organic crop production systems. Trainees included agricultural professionals from St. Croix, St. Thomas, St. John, and Puerto Rico representing the Virgin Islands Department of Agriculture, the University of the Virgin Islands Cooperative Extension Service and Agricultural Experiment Station, USDA Resource Conservation and Development Program, VI Farmer's Cooperative, St. Thomas Farmer's Cooperative, University of Puerto Rico-Mayaguez, and several prominent farmers from both St. Croix and St. Thomas. Two organic farms and members of the Virgin Islands Farmer's Cooperative have adopted production practices resulting from this grant. These practices include; incorporation of cover crops to improve soil quality, implementation of organic pest management strategies, and the utilization of vegetable cultivars that were tested during the research trial. Three PhD students and 1 MS student have been trained or funded by this project. Of these 1 PhD student and the MS student have completed their degrees. The 2 other doctoral students have completed their research and should complete their degrees in 2011. Three undergraduate students were trained in research and extension and presented a poster about their experience at the American Society for Horticultural Science Conference in Orlando in July 2008. One refereed journal article has been published and several more are in review or in preparation. Results have also been disseminated at state, regional, and national conferences. PARTICIPANTS: Dr. Xin Zhao supervised the selection and training of the undergraduate students and coordinated with Dr. Unruh Snyder who is no longer with the University of Florida. Workshops were designed by Marilyn Swisher of the University of Florida. Juan Carlos Rodriguez of the Florida Organic Growers and Consumers, Inc served as a facilitator at the workshops in Florida and the Virgin Islands. TARGET AUDIENCES: Target audiences were agriculture professionals and key growers from Florida, St. Thomas, St. Croix, St. John, and Puerto Rico. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Crop rotation, cover crops, living mulches, and intercropping used together to create more complex cropping systems were evaluated in Florida and the Virgin Islands over a two-year period. Velvet bean did not germinate well at both locations and succumbed to disease in Florida. In subsequent studies a a root-knot nematode resistant cowpea cultivar will be utilized instead. Although the cover crops suppressed weeds during the summer fallow; this suppression did not persist during the subsequent cash crops. This is probably because the weed seed bank was unchanged over the two-year study period. It is anticipated than when systems are examined over longer durations, complex systems will contribute to weed seed bank depletion and weed recruitment during the cash crops will decline. In the short term, retention of the cover crop residue as mulch on the soil surface or the utilization of other organic mulches or synthetic mulch can assist with weed management during the cash crops. Squash treated with cover crops sorghum sudangrass and pearl millet harbored significantly more parasitoids, and had significantly lower aphid populations compared with the control. Squash in sorghum sudangrass treatments had significantly more whitefly coccinellids, and had significantly fewer whitefly eggs, immatures and adults compared with the control. Summer cover crops of sorghum sudangrass or pearl millet increased root-knot nematode (Meloidogyne incognita) population levels in some instances while sunn hemp suppressed it in the broccoli-sweet corn experiment. The multiplication rate of root-knot nematodes was lowest when broccoli was planted in the cropping system. Systems with sorghum-sudangrass (alone or in mixture) increased population densities of ring (Mesocriconema spp.) and lesion Pratylenchus spp.) nematodes, and occasionally increased stubby-root nematodes (Paratrichodorus spp.). Cover crops that increased nematode numbers when planted alone usually gave the same result when planted in mixtures with another cover crop. Other cropping systems failed to suppress plant-parasitic nematodes but maintained low densities similar to weedy fallow. In St. Croix, it was determined that neither system complexity nor cover crop treatment had a beneficial effect upon maintaining high pre-experimental levels of soil nutrients (N, P, K) soil organic matter over the course of this experiment under intensive conventional soil tillage regimes in a three crop per year rotation for two consecutive years. However, it was determined that under tropical organic crop production standards, yields of tomato, totsoi, and cucumber could either equal or exceed yields of conventionally grown comparable vegetables for the State of Florida. Both spiral and reniform nematode levels decreased over time across all cover crop treatments to low or nonexistent levels. Results were disseminated during a to a diverse group of agricultural professionals from the Virgin Islands and Puerto Rico. The trainees have since returned to their respective locations to further disseminate knowledge and insights gathered as a result of this research initiative to their respective farmer constituents.

Publications

• Bhan, M. 2010. Cropping System Complexity for Suppressing Pests in Organic Vegetable Production. University of Florida PhD Dissertation.
• Bhan, M. and C. A. Chase. 2009. Weed community changes with cover crops and crop rotation in organic vegetable production. WSSA Abstracts, #476, 1 page.
• Bhan, M. and C. A. Chase. 2009. First year assessment of weed seedbanks in organic vegetable production systems in north central Florida. Proc. Florida Weed Science Society, pp. 7-8.
• Bhan, M.,R. McSorley, and C. A. Chase. 2010. Effect of cropping system complexity on plant-parasitic nematodes associated with organically grown vegetables in Florida. Nematropica 40:53-70.
• McNeill, C.A., O. E. Liburd and C. A. Chase. 2011. Effect of Cover Crops on Aphids, Whiteflies and their Associated Natural Enemies in Organic Squash. Journal of Sustainable Agriculture (In review).
• Scott, C.A. 2008. Leguminous and Graminaceous Cover Crops for the Control of Insect Pests in Organic Squash. University of Florida MS Thesis.
• Weiss, S.A., D.D. Treadwell, C.A. Chase and R. Ben Avraham. 2009. Sustainable Management of Soil Nitrogen and Organic Matter in Low-External-Input Organic Crop Production in the Caribbean. http://a-c-s.confex.com/crops/2009am/webprogram/Paper54491.html. (abstract)
• Weiss, S.A., D.D. Treadwell, C.A. Chase, and R. Ben Avraham. 2009. Effect of cover crop biomass and green manure systems on vegetable yield in low-external-input (LEI) organic crop production in the Caribbean. Caribbean Food Crops Society 45th annual meeting, Basseterre, St. Kitts, July 2009. (Poster)

Progress 06/15/07 to 06/14/08

Outputs
OUTPUTS: The second year of research in Florida and St. Croix was initiated in summer and fall 2007, respectively. Final field data collection is scheduled for summer 2008. The experiments were designed to compare different summer cover crop-fall vegetable-spring vegetable cropping systems for their effects on pest and beneficial organisms and to assess the effects of the cropping systems on soil nutrient status. Data analysis for the St. Croix location is on-going. Results are reported for the north central Florida location. Graminaceous cover crops of sorghum sudangrass and pearl millet and leguminous cover crops of sunn hemp and velvet bean were grown in summer as monocultures or as grass-legume mixtures of pearl millet-sunn hemp and sorghum sudangrass-velvetbean. Insects: The effect of the cover crops on the populations of aphids and whiteflies and natural enemies in organic summer squash was evaluated. Weeds: The effect of the summer cover crop monocultures and mixtures on weed infestation during the cover cropping period and in subsequent fall and spring cash crops was assessed. Results are reported for the first year of the study. Nematodes: One full season of nematode sampling has been completed in two vegetable production systems (cover crop-squash-pepper and cover crop-broccoli-sweet corn). Effects of summer cover crops on nematode population levels have been evaluated following cover crop, winter vegetable, and spring vegetable crops. Results were similar in each of the two vegetable production systems. Root-knot and stubby-root nematodes were unaffected by the cover crops. Lesion and ring nematodes built up on cropping systems with sorghum-sudangrass (SS), whether SS was planted alone or mixed with velvetbean. In most cases, increased levels of lesion and ring nematodes as a result of treatments with SS persisted through the fall and spring vegetable crops. Soil nitrogen: The cropping systems also were compared to determine their effects on soil nitrogen. Yields: The effect of the cropping systems on marketable vegetable yields was also compared. Results for year 1 are reported. Internships: Three interns were trained in research and extension techniques in spring 2008. PARTICIPANTS: One Masters student and one PhD student are funded by this project. In addition, three undergraduate students were provided with paid internships in which they were trained to conduct a field experiment with cover crops and a workshop was arranged to provide them with training in developing extension materials. Dr. Xin Zhao (Horticultural Sciences Department, University of Florida) has joined the project team and is assisting with the training of the undergraduate interns. TARGET AUDIENCES: The St. Croix experiment is located at the Virgin Islands Sustainable Farm Institute. The research area is used as a teaching tool for resident interns as well as visiting tour groups. Plans are in progress for the formal outreach part of the project - training of service providers and organic growers. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Insects: The grass monocultures, particularly sorghum sudangrass, have the best potential for suppressing aphid and whitefly populations in organic summer squash. Sorghum sudangrass-velvet bean also demonstrated potential to reduce pest numbers by enhancing parasitoids and predator populations. Weeds: During the summer fallow period, grass cover crops suppressed weed density and biomass more effectively than the legume cover crops. The pearl millet monoculture and biculture gave the best weed suppression. Weed densities were assessed within the planting rows in squash at 4 weeks after planting (WAP), broccoli at 3 WAP, sweet corn and bell pepper at 2 WAP. In squash, grass weed densities were the same or higher with cover crops than with the weedy control. Only the bicultures had lower densities of broadleaf weeds than the weedy control. In broccoli, grass and broadleaf weed densities were equal to or greater than in the weedy control. In spring-grown sweet corn and bell pepper neither the grass, broadleaf, nor sedge weed densities with cover crop treatments were significantly lower than those with the weedy control. Nematodes: While lesion and ring nematodes are not expected to be damaging to vegetable crops at the population levels observed, the crop rotation principles demonstrated are important for organic growers. The results indicate that the summer cover crops chosen can affect nematode numbers through the next two successive vegetable crops. Thus a good (or poor) cover crop choice can influence nematode populations in the site for the entire year. Soil Nitrogen: Dry weights for sorghum sudangrass and pearl millet monocultures ranged between 4067 to 5403 kg/ha and were similar to sorghum sudangrass-velvet bean and pearl millet-sunn hemp bicultures. Both years monoculture velvet bean biomass was low (715 and 118 kg/ha for 2006 and 2007 respectively) due to poor stand establishment. Cover crop (CC) total nitrogen (N) in monoculture sunn hemp was higher compared to remaining CC treatments both years (95 and 93 kg/ha in 2006 and 2007, respectively) but those differences were not consistently observed in soil nitrate content. Immediately prior to CC incorporation, soil nitrate to a 20-cm depth ranged from 3.9-4.0 mg/kg in 2006 and 4.3-5.5 mg/kg in 2007, with no differences among treatments. Soil nitrate following fall vegetable crop harvest was similar among all treatments in 2006, but variable in fall 2007 likely due to rotation effects. Overall, CC have the potential to offset vegetable crop N requirements, but actual CC N contribution was limited by subtropical conditions and inherent soil properties. Yields: Only the pearl millet monoculture produced higher squash and sweet corn marketable yields than the weedy control. There was no difference among cover crop treatments in marketable yield of broccoli and bell pepper. Internships: Students gained practical research and extension training experiences that will help to prepare them for careers or graduate school. Students prepared an abstract and a poster summarizing their experiences for the American Society for Horticultural Sciences meeting.

Publications

• Bhan, M., C.A. Chase, R. McSorley, O.E. Liburd, D.D. Treadwell, and W.P. Cropper, Jr. 2008. Cropping system biodiversity for managing weeds in organic vegetable production. Proceedings Southern Weed Science Society 61:130.
• Bhan, M., C.A. Chase, and R. McSorley. 2008. Effect of cropping system complexity on plant-parasitic nematodes associated with organically-grown vegetables in Florida. HortScience 43(4):1186.
• Canger, V., K. Goodell, M. Riehm, X. Zhao, C. Chase, and L. Snyder. 2008. Undergraduate opportunities in organic and sustainable horticultural research, education, and extension. HortScience 43(4):1216.
• Scott, C.A. and O.E. Liburd. 2007. Tracking insect populations within organic vegetable systems to determine how residual populations from cover crops affect vegetable production. Entomological Society of America. (Abstract)http://esa.confex.com/esa/2007/techprogram/paper_31991.htm.
• Treadwell, D., M. Alligood, C. Chase, and M. Bhan. 2008. Soil nitrogen responses to increasing crop diversity and rotation in organic vegetable production systems. HortScience 43(4):1107.